Mini-Nd:YAG Laser Illuminates Microfluids

In satellite-based synthetic aperture radar or remote sensing applications, widely spaced imaging apertures help boost resolution. Even in space, however, practical limits to how much sky a satellite can fill restrict the number and spread of sensors. Alternatively, scientists have envisioned constellations of 100 to 1000 miniature satellites flying in formation to produce better results at lower cost. Researchers at the University of California at Santa Barbara are using a pulsed Nd:YAG laser from New Wave Research to help determine how the microthrusters necessary for these minisatellites should be designed and optimized.

A dual-head Nd:YAG laser is aiding research into the behavior of microfluids in microthruster models like this one, which has a throat measuring 35 µm. Courtesy of Massachusetts Institute of Technology.The researchers coat microscopic latex seed particles with a fluorescent dye and then inject them into the nitrogen flowing through prospective microthruster designs. They double the laser's wavelength to the 532 nm at which the dye fluoresces and capture high-speed images of the emissions at the thruster's 50-µm throat. They can then use statistical methods to correlate the images and determine the design's efficiency.

Steve Wereley, a researcher on the project, said the lab selected New Wave's MiniLase II laser partly for its short pulse width and dual heads. The MiniLase incorporates two separate YAG lasers running under the same beam path that can be triggered to pulse more rapidly than more standard designs. To image supersonic flows, the researchers required a laser able to get down into nanosecond pulse separations, a range beyond many YAGs.

"Typical YAG pulses are spaced 10 to 30 Hz apart, but this one has two heads so you can fire the lasers independently of each other to get any time separation," said Wereley.

The MiniLase's compactness also contributed to its selection for this application. Otherwise, he said, "I would need two conventional YAGs and then a beamsplitter and conventional mirrors. "This is all in one box."